One of Fuyuki's most recognizeable traits is that what he lacks in physical stamina, he fills with a gentle, kind heart and an amazingly excessive ability to forgive. He is the opposite of his sister Natsumi in many ways. First of all, their personalities vary widely, since Natsumi tends to be very outgoing and quick-tempered as well as strongly athletic, whereas Fuyuki is much more calmer and reserved, and tries to avoid fighting and physical education as much as he can, but does unleash a full body of bottled anger that even frightens Natsumi when he is uncharacteristically furious. Also, their names and traditional colors are opposites, as Fuyuki's name means "winter tree" and blue is his signature color and Natsumi's means "summer beauty" and has red as her symbolic color. Fuyuki is an obsessed expert of the paranormal and science fiction, and for unknown reasons, he tends to encounter many of the bizarre creatures that he knows whenever at an episode that centers around him, most of them being quite epic. His appearance reflects that of a normal Japanese boy; black hair, dark violet eyes, and an average figure.

Fuyuki has a close bond with Keroro that exceeds space, even though Keroro is supposed to be his enemy. Fuyuki always affectionately calls him 'gunso', or 'sergeant', and they sometimes spend quality time together whether it would be playing at the park or unwittingly helping Keroro in another one of his idiotic schemes to help conquer Earth. Although Fuyuki is well-aware that Keroro is an invader alien, he always gets upset when he catches him plotting or scheming and uses one of his signature lines, "Aren't we friends?!" to weaken Keroro. He is also the one to always stop the sergeant whenever the alien's plan is to completely destroy Earth, saying that if the Earth is blown away, so will all the Gundam model factories, as Gundam-making is one of the sergeant's most obsessive hobbies. He is also responsible on keeping the Kero-ball away from the sergeant, since it is a devastatingly dangerous but strange Keronian weapon that Fuyuki sometimes uses as a toy/weapon.

Fuyuki also has a unique bond with Alisa Southerncross, since Alisa always uses Fuyuki as bait to attract aliens, or "dark" or "cursed ones", as she and her father calls them. Although any other person would've absolutely hated this position, Fuyuki forgives Alisa about this, since Alisa was actually a puppet and her father thought that by hunting aliens, she would eventually gain humanity.

Their bond often infuriates Momoka Nishizawa, his classmate, who has an amorous crush on Fuyuki and often comes up with plots to attract his attention (humorously, these often-failing plots are a major part of the series' comedy). Fuyuki doesn't seem to feel any romantic feelings toward Momoka, since he always calls her "Nishizawa-san", a proper term to address a stranger or someone who is high in social class (as Momoka is extremely affluent). However, he does love her as a close friend and would never abandon her.

Despite his unearthly patience with the insanity that seems to flower in the wake of Keroro and the others, Fuyuki does have a temper. When his temper is up, which admittedly takes A LOT, Fuyuki is capable of terrorizing not only Keroro and the platoon but his sister and regular people as well. Source - Wikipedia